I don't actually know him (I didn't comment on that thread), and I'm not claiming my fear is rational. Yes, the result of blinding yourself is that you run the risk of making the world worse and hurting people in the process, including the people that were trying to help.

If you're unhappy with being a scientific racist (I hate that term - if it describes the way the world is then its just science) then maybe you should take a look at the other side of the debate. Then again, some people might accuse Kees Jan Kan of being racist for acknowledging the IQ differences, even if he argues against genetic causes.

The knowledge matters because people have been trying for decades to equalize outcomes for different groups - in terms of achievement and crime. If this is not possible, and there are casualties in the cross fire (say teachers getting fired for not getting minorities to perform at the same level) then we need to change our approach. If you could acknowledge that the causes of violent crime are biological in nature and then suggest biological interventions (someone on LessWrong recently suggested fish pill oils to correct for micronutrient deficiencies), how many lives would be saved? How many people would be spared a life of crime? If you could acknowledge that culture problems and social multipliers have huge effects on adult criminality and success, and make policy decisions based on that (although this problem is very difficult) how many more lives could be saved? If the political climate only allows you to say that different outcomes are the result of the discriminatory schooling system, those nasty racists and the prejudiced authorities - then your interventions aren't going to work and there will be needless casualties. The knowledge certainly does matter.